Understanding how much you can afford for a mortgage is a crucial first step in the home-buying process. This calculator helps you estimate your maximum affordable mortgage payment based on your income, debts, and desired down payment. Remember, this is an estimate, and lenders will consider many other factors.
.calculator-container {
font-family: sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 500px;
margin: 20px auto;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 15px;
}
.calculator-container p {
font-size: 0.9em;
color: #555;
margin-bottom: 20px;
text-align: justify;
}
.input-section label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #444;
}
.input-section input {
width: calc(100% – 20px);
padding: 10px;
margin-bottom: 15px;
border: 1px solid #ddd;
border-radius: 4px;
box-sizing: border-box; /* Include padding in width */
}
.calculator-container button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 1em;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 10px;
}
.calculator-container button:hover {
background-color: #0056b3;
}
#result {
margin-top: 25px;
padding: 15px;
border: 1px solid #d4edda;
background-color: #d4edda;
color: #155724;
border-radius: 4px;
font-size: 1.1em;
text-align: center;
font-weight: bold;
}
function calculateMortgageAffordability() {
var annualIncome = parseFloat(document.getElementById("annualIncome").value);
var monthlyDebt = parseFloat(document.getElementById("monthlyDebt").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(annualIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
annualIncome <= 0 || monthlyDebt < 0 || downPayment < 0 || interestRate <= 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// General affordability guidelines (common lender ratios):
// Debt-to-Income (DTI) ratio is a key factor. Lenders typically look for a front-end ratio (housing costs)
// of around 28% and a back-end ratio (total debt including housing) of around 36%.
// We will use a conservative approach for this calculator.
var maxMonthlyHousingPaymentRatio = 0.28; // Max percentage of gross monthly income for housing (PITI)
var maxTotalDebtRatio = 0.36; // Max percentage of gross monthly income for all debts (including PITI)
var grossMonthlyIncome = annualIncome / 12;
// Calculate maximum allowed total monthly debt payments
var maxAllowedTotalDebt = grossMonthlyIncome * maxTotalDebtRatio;
// Calculate maximum allowed monthly mortgage payment (including PITI – Principal, Interest, Taxes, Insurance)
var maxAllowedHousingPayment = grossMonthlyIncome * maxMonthlyHousingPaymentRatio;
// Subtract existing monthly debts to find the maximum affordable P&I (Principal & Interest) portion
// of the mortgage payment. Taxes and insurance are *additional* to P&I.
// We'll estimate a buffer for taxes and insurance, as this is a simplified calculator.
// A common estimate for PITI is around 1.2% of the home value annually (for taxes, insurance, PMI if applicable).
// For simplicity in this calculator, we'll aim to find the P&I portion, assuming taxes/insurance will be factored in by the lender.
// So, the maximum P&I payment is essentially our maxAllowedHousingPayment minus an estimated buffer for taxes/insurance.
// A safer approach for estimation is to directly calculate P&I based on maxTotalDebtRatio,
// as it already accounts for all debts.
// Let's refine: Maximum P&I payment is the difference between the max total debt allowed and existing debts.
var maxMonthlyPrincipalInterest = maxAllowedTotalDebt – monthlyDebt;
// If existing debts already exceed the total debt limit, affordability is zero.
if (maxMonthlyPrincipalInterest <= 0) {
resultDiv.innerHTML = "Based on your income and existing debts, you may not qualify for a mortgage.";
return;
}
// Now, we need to work backwards to find the maximum loan amount that results in this P&I payment.
// The mortgage payment formula is: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Where:
// M = Monthly Payment (maxMonthlyPrincipalInterest)
// P = Principal Loan Amount (what we want to find)
// i = monthly interest rate (annualRate / 12 / 100)
// n = total number of payments (loanTerm * 12)
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
// Rearrange the formula to solve for P:
// P = M * [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var numerator = Math.pow((1 + monthlyInterestRate), numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow((1 + monthlyInterestRate), numberOfPayments);
if (denominator === 0) { // Avoid division by zero if interest rate is 0 (though validation prevents this)
resultDiv.innerHTML = "Invalid interest rate.";
return;
}
var maxLoanAmount = maxMonthlyPrincipalInterest * (numerator / denominator);
// Calculate the maximum affordable home price
var maxAffordablePrice = maxLoanAmount + downPayment;
// Display results
var formattedMaxLoanAmount = maxLoanAmount.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxAffordablePrice = maxAffordablePrice.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxMonthlyPrincipalInterest = maxMonthlyPrincipalInterest.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
resultDiv.innerHTML = `
Estimated Maximum Monthly Principal & Interest Payment: ${formattedMaxMonthlyPrincipalInterest}
Estimated Maximum Loan Amount: ${formattedMaxLoanAmount}
Estimated Maximum Affordable Home Price (including down payment): ${formattedAffordablePrice}
Note: This estimate does not include property taxes, homeowners insurance, or Private Mortgage Insurance (PMI), which will increase your total monthly housing cost.
`;
}